Dichroic filters, also known as interference filters, are constructed by depositing one or more layers of metallic and/or dielectric films with precise thicknesses to produce filters which transmit certain wavelengths of light and reflect others. The colors of a dichroic filter can be predicted and manufactured to match spectral functions such as the CIE tristimulus curves s (e.g. the 1976 UCS standard chromaticity diagram), and such filters enable purer color filtering, reflection and transmission compared to gels due to their higher extinction ratio at wavelengths which are blocked and higher transmission at wavelengths that are passed. Dichroic filters are temperature stable from a range of about −80 degrees to 700 degrees F. They absorb less than five percent (2%) of the light transmitted through them as they are primarily rejecting out of band wavelengths through reflection. And, for in band wavelengths, they exhibit greater than ninety percent (90%) transmission thus requiring less power to achieve greater brightness. The above process is disclosed in U.S. Pat. No. 5,711,889, Method For Making Dichroic Filter Array, which is hereby fully incorporated into this specification.
The object of the present invention disclosed in this patent application is the application and patterning of a photosensitive material as outlined in U.S. Pat. No. 5,711,889 but leaving off several dichroic layers and replacing them with a coating such as an anti-reflective or other metallic or dielectric film coating to complete the spectral characteristics desired. In an alternative embodiment the coating can be applied first with the patterned dichroic layers added on top of the coating.
U.S. Pat. No. 5,756,239, Wake, May 36, 1998, Method of Forming a Color Filter Array With Improved Resolution, discloses a method for use in forming a high resolution color filter array the following steps are used: coating a colored layer containing a binder, a colorant in the binder, the binder being transparent over the entire visible electromagnetic spectrum and remaining so even after extended treatment with elevated temperature and light; hardening the colored layer; providing and patterning a photoresist layer over the hardened colored layer; and treating the patterned photoresist layer so that it is selectively resistant to oxygen plasma etch. Further processing steps are used to complete the colored filter array. U.S. Pat. No. 5,954,559, Holmberg, Sep. 21, 1999, Color Filter Structure and Method of Making, discloses an improved planar color filter structure to reduce defects in the display devices incorporating the color filter structures, including active matrix displays. A color filter substrate has a thicker polyamide black matrix formed thereon and a transparent polyamide layer formed over the black matrix. The transparent layer is exposed through the black matrix and developed to remove the unexposed portions over the black matrix. The resulting surface is substantially planar and facilitates the forming of the remaining layers to form a substantially planar color filter structure. These patents disclose use of dyes and gels patterned to form the color filter. No dichroics are used.
U.S. Pat. No. 5,889,227, Hawkins, et al, Mar. 30, 1999, Planar Color Filter Array For CCDS With Embedded Color Filter Elements, discloses an image sensor and method of making such sensor. The sensor includes an integral color filter array, comprising: a semiconductor substrate having an optically planar top surface; a plurality of spaced image pixels formed in the substrate; and an array of physically contiguous color filter elements embedded in the substrate whose top and bottom surfaces are coplanar and which have no overlap of color filter layers between adjacent color filter elements. This patent discloses a planar filter element created by etching rather than the liftoff method disclosed U.S. Pat. No. 5,711,889, and thus is difficult to manufacture.
Also, a number of patents have been issued that disclose using dichroic filters with detectors. U.S. Pat. No. 5,942,762, Hecht, Aug. 24, 1999, CCD Scanner Having Improved Specular Reflection Discrimination, discloses an optical scanner that utilizes two linear CCD detectors and a bandpass means to improve the ability of the scanner to discriminate against specular reflection. A coded symbology is illuminated by a noncoherent light source and light reflected from the coded symbology along a first path strikes the front face of the bandpass means. The bandpass means, functioning as a notch filter, transmits a select bandwidth of light while reflecting all other light onto a first CCD detector. Simultaneously, light reflected from the bar code symbol travels along a second path, at a different angle with respect to the plane of the coded symbology than the first path, is reflected from a mirror onto the back face of the bandpass means. The bandpass means transmits the select bandwidth of light onto a second CCD detector and reflects all other light. The second CCD detector has a notch filter which permits the detection of only the select bandwidth. Since specular reflection is only experienced at a single angle, with respect to the plane of the coded symbology and each CCD detector detects an image at a different angle with respect to the plane of the coded symbology, a complete image can be reconstructed by combining information obtained from both CCD detectors. But this patent does not disclose patterning which includes coating to complete the spectral requirements.
The combination of dichroic filters and other filters, such as anti-reflective filters is typically used in lighting projectors and is usually accomplished as shown in U.S. Pat. No. 6,623,144 which discloses a high intensity light projector for stage, architectural and similar applications includes a controllable image quality projection gate providing advanced visual effects. The projection gate, capable of selectively scattering or transmitting incident light, may be constructed of an array of scattering liquid crystal material in combination with infrared and ultraviolet reduction means which provide in the high intensity beam, a stable thermal environment by minimizing the absorption of light by the projection gate. Additional thermal efficiency is provided by supplemental cooling means. Color control is also provided in the form of dichroic filter wheels forming cooperating adjustable low, high and band width filters including saturation control. A color measuring feedback sensor is also provided. An intensity measuring feedback sensor controls a spatially-modulated, variable-density, reflectively-coated dimming wheel. A programmable gobo system has provisions for gobo selection, orientation, and rotation.
Another example of these types of projection systems is disclosed in U.S. Pat. No. 5,168,351, which discloses a video color image projector that includes a block of crossed dichroic mirrors for combining the light rays from image rasters on respective monochrome image display devices and a projection lens for projecting the composite color rays so as to form an enlarged color image on a display screen. Each display device has a faceplace which is convex on the interior surface thereof and having thereon an interference filter in the form of an internal angularly reflecting coating (IARC). Each faceplate is liquid—coupled to a negative power lens element, so that the faceplate, coupling liquid (or gel) and such lens element effectively constitute a single negative power field flattener lens at each entrance side of the dichroic block. The composite color rays at the exit side of the dichroic block are projected on the display screen by an assembly of lens elements which includes at least one optically positive lens element. The focal length of the complete projection lens formed by such assembly and each of the negative field flattener lenses may be from 0.5 to 0.9 times the diagonal D of the image raster on each display device, so that the projector is sufficiently compact to be included in a cabinet suitable for consumer television receivers. This patent also does not disclose patterning which includes coating to complete the spectral requirements